AC problem appears to be legit. :(
System is a Carrier Infinity heat pump (25HNA648A003) that was installed 6/26/2008. Error codes are 77 (High Stage - No Start) and 78 (error code 77 three times in a row).
Waiting for ADCO HVAC guys that originally installed the system to call me back. Anyone in the Warrenton area know a decent HVAC company that they can recommend?